In what is referred to as thermo-mechanical rolling of coarse steel the rolling process attempts to produce a structure which is as fine-grained as possible, in order to optimize the mechanical properties of the end product. The rule of thumb applies that the mechanical properties are all the better, the finer the grain is. The principle of thermo-mechanical rolling consists of destroying the coarse grain which forms during the heating up of the coarse sheet to be rolled or during rolling at high temperatures, by reshaping to the intermediate thickness and to prevent a growth in grain by temperature reduction. It is typically important in this context to reshape the material completely (strain penetration), in order also to influence the structure in the material core. This may be done most effectively by reshaping which is as great as possible per stage. If it is not possible to work with maximum reshaping in all stages, the stages before the cooling pauses and in the rolling phases with low temperature are preferably maximized.
In order to achieve the highest possible degrees of deformation, the use of especially large and strong roll stands and roll drives is known in the art. However, these measures are typically very cost intensive and cannot be used for modernization projects in particular. As an alternative or in addition an attempt can be made with adjustment elements which influence the course of the rolling gap (for example roles displacement and roll deflection) to keep the level of the rolling force high up to the last reduction stages. Both measures nevertheless shift the limit up to which deformation can take place, a deformation limit still remains which cannot be exceeded.
A method is also known in which an attempt is made to roll the rolling stock in consecutive stages with increased rolling forces to the intermediate thickness. This method is named after its inventor (Malcolm Gray). The basic idea of this method is to maximize the deformation and thus the strain penetration up to the end of rolling from stage to stage, since here the effect in respect of the structure formation is at its greatest. If it can be carried out without modification the method leads to results which are better than those of the conventional method described above. If however problems arise during rolling which lead to an unforeseen increase in the required rolling force or the like, the method is significantly worse than other conventional techniques. This is because in this case a further stage with generally only a small degree of deformation must be added to the path carried out with a high degree of deformation so that the desired intermediate thickness is obtained.